Retractable assemblies are widely applied in analytical measurements technology. They serve to withdraw sensors from the process, and therewith from the medium, without process interruption and then to reintroduce them back into the process. The sensors are held in an immersion tube and moved by means of a drive manually or automatically, for example, pneumatically, axially between a process position and a service position. These procedures run within a determined timing cycle or as a function of other determinable or measured parameters.
Sensors for use in this invention include sensors for measuring one or more physical or chemical, process variables.
If retractable assemblies are used for accommodating the sensor for determining at least one process variable, the sensor can be checked, calibrated, cleaned and/or replaced in the service position, wherein the sensor is located, in such case, in a handling chamber arranged in the housing of the retractable assembly.
Retractable assemblies are manufactured and sold by the group of firms, Endress+Hauser, for example, under the mark/designation, “Cleanfit H CPA475”.
The field of use of retractable assemblies for measuring physical or chemical, process variables of a medium, e.g. a fluid, especially a liquid, in process technology is all encompassing. Used for determining the process variables are sensors, examples of which include pH sensors, conductivity sensors, optical or electrochemical sensors for determining a concentration of a substance contained in the medium to be monitored, e.g. substances such as O2, CO2, certain ion types, organic compounds, or the like. The medium can, in given cases, be a critical medium. The terminology, critical, means, for instance, that the medium is valuable, expensive, combustible, corrosive, poisonous, aggressive, hot, cold, bio-endangering, radioactive, etc.
In all cases, it is to be heeded that no medium escapes from the process. Especially, care must be taken that the sensor is not deinstalled when the retractable assembly is located in the process position, since otherwise a connection from the process to the environment is created.